Process for separating potassium and sodium hydroxides



Patented Nat. 24,1925.

UNITED STATES THEODOR suTTnn', or moNTHnY, swiTznnLA iIn, ASSIGNOB To THE FIRM socIETY or CHEMICAL INDUSTRY IN BASLE, or BASEL, SWITZERLAND.

rnocnss non snrnnnrme roTAssIi' nI AND somum nxnnoxrnns.

No Drawing.

To all whom it may-concern.

Beit known that I, THnonoR'SUTTEn, a citizen of theSwiss Confederation, residing at Monthey, Switzerland, have invented a new and useful Process for Separating Potassium and Sodium Hy droxides, of

which the following is a full, clear, and

exact specification. H

A'process for the separate separationof potash and soda from their mixtures in aqueous solutions, has not hitherto been known notwithstanding, that mixtures of these alkalies occur in various technical processes and their complete separation or.

' the enrichmentof the solution in one or other of thecomponents for the purpose of obtaining a desired composition of the mixture is a great technical importance When aqueous mixtures of the two alka- --lies, containing for example equimolecular proportions of potash and soda, are evapo- .rated untilcr stallizationoccurs on cooling the mixtureo crystals obtained has approxi- 'orderto separate potassium hydroxide, the

m'ately the composition of.the parent material, so that it might be supposed that the hydroxides-or hydroxyhydrates'of the alkalies crystallize like the carbonates in the form of molecular compounds of the bases. The present invention relates to a process for separating mixtures of potassium and sodium hydroxides, according to which, in

mixture is concentrated until crystallization occurs in part at relatively high temperature, whereupon the potassium hydroxide crystals formed are eliminated from the mother liquor also at raised temperature, and, in order to separate sodium hydroxide the mixture is diluted in such a manner that partial crystallization occurs only at rela I tively low -'tempei"ature,wh'ereupon the so-' dium hydroxide crystals formed are elimi-. nated from the mother liquid also at low temperature. r a f It has been found that a practically pure potassium hydroxide crystallizes from mixtures or solutions relatively rich in potassium hydroxide above certain concentrations and temperatures which vary according to 'tl1e,c6mposition of the mixtures,.while the hydrated sodium hydroxide remains in.

j liquid condition. I .By centrifuging .the crystals a mother liquor is obtained which is considerably poorer in potassium hydrox- Application filed May a, 1925; Serial No. 28,951.

ide than the original mixture By further cooling ofthe liquor crystals separate which are considerably richer in sodium hydroxide than the originalpliquor but still containing considerable quantities of potassium hydroxide. If, however, the mother liquor is first diluted after separation of the potassium hydroxide, and then cooled, almost pure crystals of hydrated sodium hydroxide separate. The remaining mother liquor has approximately the composition of the original liquor. It can be brought again to the original composition and subjected to the same treatment.

As a rulethe alkali which revails more or less in. the-mixture is pre erably eliminated first, If for instance there is in the mixture less tha'n'35% of potassium hydroxide, the sodium hydroxide is eliminated first.

Mixtures containing more, than 35% of po tassium hydroxide are treated first in order to separate the most potassium hydroxide possible, wherea-fter the sodium hydroxide is separated from the mother liquor.

In order further to purify the crystals, they may be dissolved in a smallquantity of water and the process of separation reposted at a suitable temperature and concentration.

It is clear that the invention isalso applicable for obtaining aqueous mixturesof potassium and sodium hydroxides of desired composition in respect ofcontent of these two hydroxides, or to enrichmg such a mix ture in eitherconstituent as may be suit able for any particular technical purpose.

' The followingjexamplfeis illustrate the in- I 1 vention:- r v I Emample '1- L A purified alkali solution containing equal parts by .Weight of potash" and soda is evaporated to 60 Baum and stirred with bladesat about 60 C. in acrys'tallizing'vat until there is no further increase of crystals. The mass is. thoroughl centrifuged in a heated centrifuging mac, ne whereu on the separated erystalscconsist of ractica y pure hydrated potassium hydroxi e. The mother iluted to about" 55" Baum and liquor is stirred, w ile cooling by meansof flowing water. The separated crystals contain only 8-10 per cent of otash, while the mother a liquor contains it out .50 per cent. This liquor maybe again concentrated to 60 weight of potash and Baum and treated further in the same manner.

Example 2. An alkali solution containing parts by 70 parts by weight of soda is diluted at about 50 C. to about 56 Baum and cooled while stirri'n There separates nearly pure hydrated sodium hydroxide which can be freed fro the residue of adhering potash by corresp nding dilution and. fresh crystallization.

Example 3.

An alkali solution containing 60 parts of potash and' lO parts of soda is concentrated to 61 Baum, and crystallized at 70 C. The centrifuged crystals contain over 90 per cent of potash.

Example 4. 7

separation of mixtures of potassium hy-- droxide and sodium hydroxide, according to g which, in order to separate potassium hyhydroxidc, the

droxide, the mixture is concentrateduntil crystallization occurs in part at relatively high temperature, whereupon the potassium hydroxide crystals formed are eliminated from the mother liquor also at raised temperature, and, in order to separate sodium i droxide, the'mixtu're is diluted in such a manner that partial crystallization occurs only at relatively low temperature, whereupon the sodium are eliminated from the mother liquor also at low temperature. i

2. The herein described process for the separation of mixtures of potassium hydroxide and sodium hydroxide, according to which, in order to separate potassium hyhydroxide crystals formed droxide,. the mixture is concentrated until crystallization occurs .in part at relatively high temperature, whereupon the potassium hydroxide crystals formed are eliminated from the mother liquor also at raised temperature, and, in order toseparate sodium mixture is diluted in such a manner that partial crystallization occurs only at relatively low temperature, whereupon the sodium hydroxide crystals formed are eliminated from the mother liquor also at low temperature, the alkali prevailing in the mixture being separated first.

In witness whereof I have hereunto signed my name this 21st day of April, 1925. THEODOR SUTTER. 

